Apparatus for producing porcelain enamel



June 2, 1953 R. E. SKINNER ET AL 4 Sheets-Sheet 1 Filed Dec. 2, 1950 Q mm INVENTORJ J. SKIN/V52 .94 0

7085K GL:

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June 2, 1953 R. E. SKINNER ETAL 2,540,859

APPARATUS FOR PRODUCING PORCELAIN ENAMEL Filed Dec. 2, 1950 4 Sheets-Sheet 2 j irilw INVENTORS BY lV/V KIWI/V77)?! ATTo 724/576 June 2, 1953 R. E. SKINNER E-TAL 2,640,859

APPARATUS FOR PRODUCING PORCELAIN ENAMEL Filed Dec. 2, 1950 4 Shets-Sheeii s A mmvfolgs I mam TJ. JI/IV/Yfi? a By 540v H. M/W174i, A

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J 5 R. E. SKINNER ET AL 2,640,859

APPARATUS FOR PRODUCING PORCELAIN ENAMEL Filed Dec. 2, 1950 4 Sheets-Sheet 4 Jig. 6

INVENTORS POBZPT J. .Slf/N/VEE Mo BY GLEN/V h. IA/TYRE.

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Patented June 2, 1953 [TED STATES OFFICE APPARATUS FOR PRODUCING PORCELAIN ENAMEL Robert E. Skinner, Fairview Park', and Glenn H. McIntyre, Cleveland Heights, Ohio, assignors to Eerro Corporation, a corporation of Ohio- Application December 2, 1950, SeriaLNo. 198,790

2 Claims. 1:

This invention relates as indicated to smelters for porcelain enamel frit characterized particularly in that the raw batch components from whichthe frit is e-ventuallyproduced are melted by passing electric current through the mass so that the batch is heated a's a result of its own internal electrical resistance.

The'use ofelectri'c smelters for the purpose of reducing various types of raw materialsto a molten state is 'quite old, and to a minor degree that type of heatingha s been employed for the production of conventional glass.

Porcelain enamel is,-ho wever; a very complex mixture of variousme'tallic oxides and the like so that frequently the silica content of the batch is only a minor proportion of the total. It has beenthe general practice in most electrically heated glass tanksto deposit the raw material centrally 'of the tank with electrodes spaced rather uniformly about the. space occupied by the batch and to then provide a submerged 'outlet-leading to a fining chamber fromwhich the glass is ultimately discharged. We'have foundth'at none of those glass: tanks are suitable for the smelting of porcelain enamel f-ri't in the most efficient manner. glasstanks have been patterned largely after the general principle of construction of electric furna'ces employed, for example, in the smeltingof' Other objects of the invention will appear as the description proceeds.

Tothe accomplishment of the foregoing"; and.

related ends, said invention then comprises the" features hereinafter fully described and particularlypointed out in the claims, the following dc scription and the annexed drawingssettin'g'forth' in detail certain illustrative embodiments" in the" invention, these being indicative,- however; of but a few of the various Ways in which the principle of the invention may-beemployed.

In saidannexeddrawings:

Fig. 1 is a top plane viewof a. smelter constructed-in accordance with the principles of'our invention, but in which'the-roofstructures are W hereas' these previously usedshown removed for more clear illustration of the internal structure of the smelter;

Fig. 2'is 'alongitudinal vertical section view of thesmelterillustrated in Figure 1;

Fig. 3 is a transverse vertical section View of the smelter illustrated in the previous figures taken on the plane-"substantially indicated by line Ii -3 inFigu're 2; I

Fig. 4 is a transverse vertical section 'view of the smelter illustrated in previous figures taken on the plane substantially indicated'by the line 4 40i Figure 2;

Fig. 5 is a transverse section View of the smelter illustratedin previous figures taken on the plane substantially indicated by line 5- 5 of Figure 2'; and

6 is a transverse section view of the smelter illustrated inp'reviousfigures taken on the plane substantially indicated by line B -6 of FigureZ.

Referring more specifically to the drawings and more especially to Figs. 1 and 2, the smelter herein illustrated comprises a substantially rectangular lined'melting chamber generally indicatedat l which-is formed of two vertical side walls-2 and 3 and first and second end walls 4 andi-said second end wall 5 extending downwardly 'andtermi-nating about the normal bath level. Adjacent end wall 5 there'is provided a hollew skimmer wall 6, through Which a cooling medium such as water may be circulated, and which extends downwardly terminating slightly below the normal bath level. The hearth l of themelti'ng chamberis arranged at a level substantially lower than hearth of the remaining portion of the smelter.

r The' rn'aterial to be melted is fed to the melting chamber by feeder 9- which is situated on the lateral airis of's'aid melting chamber opposite skimmer wall '6 In the preferred embodiment of our invention the feeder't'is substantially of the" same width as the inside dimension of said melting chamber and is so constructed as to contin'uousl y deliver a relatively thin layer of raw 4 batch acrossth'e surface of the molten bath. In

thls man'ner the molten bath is continually covered with ablanket of raw batch thus eliminatmg the necessity of a roof over that portion of the's-melter, since'thecovering of raw material acts as an insulating blanket preventing loss of heat and fumes; However, if wanted or deemed necessary it is entirely within the contemplation of thepreseht invention to provide a roof for the melting chamber;

the position adjacent the chamber which was just described is a smelting chamber generally indicated at H], which as most clearly illustrated in Figure 1 comprises side walls H and I2 and end wall I3, the wall 5 of the melting chamber also acting as an end wall for the smelting chamber l0. Supported on the walls is a roof 14 which may be arched or fiat and which is provided with a stack opening l5. The fioor of the smelting chamber indicated at I6 is, as previously mentioned, at an elevation which is substantially higher than the bottom of the melting chamber. The edge of the floor of the smelting chamber adjacent the passageway 8 through which the preliminarily melted material as received by the smelting chamber from the melting chamber is relieved as at H in order to reduce fioor resistance.

It is necessary at this time to note three important features of the smelter of the present invention. First, as previously pointed, the melting chamber is provided with a bottom which is substantially lower than the floor of the remaining portion of the smelter. This construction serves the important purpose of allowing the melting material to circulate thus promoting homogenization of the many different ingredients which go to make up a porcelain enamel. Secondly, the melting material as it circulates, comes up under the skimmer wall thus skimming the unmelted material and preventing it from being carried over into the smelting chamber. The next important feature is the relatively large diameter passageway between the melting and smelting chambers. One of the big troubles in making an electric smelter for the production of porcelain enamel is the prevention of a crust formation over the top of the melting raw batch. The crust is formed by the escaping volatiles and heated gases. Since the raw batch is heated from the bottom up and there is a minimum of heat at the extreme top of the raw batch, the escaping volatiles tend to solidify at the top of the raw batch forming a crust, and the crust in turn prevents incoming raw materials from reaching the lower hot zone of the melting chamber. However, with the relatively large passageway between the melting and smelting chambers there is ample room for the passage of the volatiles and heated gases to pass unimpeded towards the stack opening. The stack opening being situated at the end of the smelting chamber furthest from the melting chamber causes a draft which sucks the volatiles and heated gases towards itself and thus substantially prevents the volatiles from trying to escape through the layer of unmelted raw material.

The third important feature of the present invention is the provision of separate melting and smelting chambers. In the previous methods of electrically melting porcelain enamel the melting and smelting of the raw ingredients were carried on in the same chamber. This necessitated retaining the melted ingredients in the combined melting and smelting vault for a relatively long time until it was sufficiently smelted to go into the final fining and discharge chamber. However, with the arrangement of the present invention the raw material is preliminarily melted in the first or melting chamber and is received by the smelting chamber in a substantially completely molten condition, here the material because of its molten state is quickly and readily smelted to substantial completeness, when it then is carried into the final fining and discharge chamber where it only has to remain a relatively very short time. Furthermore by the time porcelain enamel passes through the final chamber where it receives its final fining it is virtually impossible for the discharging porcelain enamel to contain any unmelted material. We have found that by the use of a smelter of this type We have been abl to at least double production using the same electrical input and surface area as used with previous smelters.

Adjacent the smelting chamber last described is a fining and discharge chamber generally indicated at [B which comprises side walls, l9 and 20 and end wall 2 I, the wall 13 of the smelting chamber also acting as an end wall for the fining and discharge chamber IS. The fioor of the fining and discharge 22, as previously stated is on the same level as the floor of the smelting chamber l0. Supported on the walls of the chamber 18 is a roof 23 which may be arched or flat.

The submerged passage 24 which connects the smelting chamber [0 and the fining chamber I8 is so constructed as a last precaution against any unmelted material passing into the final chamber.

The principal gases which pass upwardly through the stack are the air streams which enter the smelter through its openings. In this connection any air which enters the fining and dis charge chamber passes through the passageway 25 which is formed on the axial line of the smelter directly above passageway 24. It will thus be observed that the flow of gases or heated air is substantially counter-current to the flow of the molten porcelain enamel. This is important since this sweep of air precludes any unsmelted finely divided material finding its way into the fining and discharge chamber.

In the wall 2! of the fining and discharge chamber l8 there is provided a passage 26 on the longitudinal axis of the smelter through which the finished material is discharged over a trough like extension 2! which permits the finished material to drop vertically either into a water bath or into the space between parallel quenching rolls. The entire body of the smelter is preferably formed of refractory material usually used in the construction of equipment of this kind. It is well known, of course, that in such construction the body of the structure is made of appropriate refractory blocks and the surfaces such as the hearth of the melting chamber, the side walls of the smelting and fining chamber and the floors of the chambers are all lined with special refractories, particularly suited to withstand attack from the material produced by the smelter. The details of such construction which is indicated as conventional in the art has not been shown.

The in-coming raw material is fed into the smelter, by feeder 9, at a rate substantially equal to the discharge rate of finished molten material. As best shown in Fig. 6 the raw material 28 is deposited into the melting chamber in an even relatively thin layer with no piling up of raw material in the center and with a minimum of raw material pushing under the surface of the molten material. This method of feeding forms an adequate insulating blanket over the molten material present in the melting chamber while at the same time affording ease in melting.

The raw material is reduced to finished form y being heated electrically by its own internal resistance. This is accomplished by the arrangement in the smelter of a plurality of electrodes. The first pair of such electrodes comprises those indicated at A and A which are substantially rectangular plates pported by being secured to the inner ends ofrods Y29 and 30:.respectively; The. latter rods project outward-1y through: openings The." openings through which .the supporting; rods thus" provided 1 therefor in, the: :walls :2 and. 3.

pass are well below the. :bath .level in :the smelter,

thus insuring; that theelectro des :will not become? oxidized since they are at all timescovered with molten material. Rods '29 and-30 which conduct current to-electrodes -A-and .A' are cooled .as by water.

ity of paired electrodes in the smelting chamber,

in the preferred embodiment of our invention. we usethe above mentioned three phase system. When using the three phase system we have found that a hot spot occurs.approximatelyin the center. of the triangleformed by the electrodes. This hot-spot condition-causesza-mechan-ical turbulence of the molten material-Which tends to break up any crust formation. As best shown in Fig. l the electrodes B, B and B are spaced substantially equidistant from each other forming an equilateral triangle. Therefore the current in passing from one electrode to the next forms a path which is approximately circular in a horizontal plane. As previously mentioned there is a hot spot formed approximately in the center of the electrodes. Since the hot Spot cannot be readily dissipated the molten material closest to this spot becomes hotter than the surrounding material causing it to rise, and thus causing the molten material to circulate in a vertical plane. It can now be seen that a stirring action is set up whereby the formation of a crust is held at an absolute minimum. The formation of a crust is so highly undesirable that the aforementioned system of electrodes is preferred as added insurance.

The final set of electrodes indicated at C and C are arranged in walls l9 and 20 below the bath level. Current is supplied to these electrodes through water cooled rods 33 and 34, as in electrodes A and A from a single phase circuit. It will be noted that these electrodes C and C are closely adjacent to the passage 24 in order to maintain the bath in a highly fluid state and also as added insurance that any material which may not have been fully smelted will be fined to the proper degree before passing through discharge passage 26.

In the preferred embodiment of our invention we use a separate circuit and transformer for each set of electrodes in each of the chambers. In this manner the electrical input of each chamber is controlled according to individual need.

In the selection of the material from which the electrodes are to be made care should be exercised in order to prevent their reduction by the material being smelted. It has been found that the material from which are made those portions of the electrodes which are actually in contact with the material being smelted should be lower in the A layer of chilled material-surrounds the: cooled pipes at. thewpoint where they are inserted through the walls of. the smelter, thusypreventing.

Currentirom I elect-romotive: series thanthe materialswwhich are present in the raw batch, in; the form of oxides. Thus, for example, whensmeltingia'frit batch containing substantial amounts-of zi-rioO-- nium,..i*t is desira'b-le to use-an el'ectrodez'madeiof molybdenum. While graphite I electrodes: can be:

used, especially when smelt-ingcertain, typescf p rcelain enamel, .such': as ground: coat enamels:

containing; substantial amounts of cobalt. and

nickel-oxides, best results will be secured by-the use ofv metallic electrodes selected in the mannen described.

A- further feature :of our construction is the archambers Inthis position the'stack' causes adraft" strongi'enough. to drawthe volatiles and-heatedgasesstr rough -.passag-eway 8- while-simultaneously adore-ling. :a dratt to from "chamber- Hi thus chamber-"l 8-;

In the. preferred embodiment of our invention I we maintain a temperature;differential between the melting and. smelting, chambers. By. the use of thesseparatecircuits, for each chamber weare able to, maintain the overalltemperature of the smelting-chamber: of from about 50 F; to, about:

F. higher than the overalIJtemperature of the melting chamber. Aspreviously pointed :out: the smelter is so constructed as to allowthe'tp'as sage of the volatiles and heated gases to pass unimpeded from the melting to the smelting chamber. By maintaining the above mentioned temperature differential we have found that a turbulence is set up between the two chambers, which turbulence acts as a means for causing the volatiles and heated gases to be carried over from the melting to the smelting chamber and the higher temperature of the smelting chamber causes the volatiles and heated gases to rise to the surface where they are carried off by the effects of the stack.

The subject matter of this application is related to that of copending applications Serial No. 81,478, Serial No. 239,108 and to Patents 2,559,- 683 and 2,610,217 which were copending herewith, all having the same assignee as this application.

It is preferable to provide a stack height as compared with the other critical factors so that the stack just above the roof of the smelter has at least a slight negative pressure. Since the smelting operation is performed by the passage of current through the mass, there is very little loss of raw material as by decomposition, which must be carried away by the stack. In this connection it is a notable feature of our invention that by heating the raw material by the passage of current therethrough there is very considerably less loss of raw materials due to decomposition than in the other types of conventional smelting wherein the mass is heated by a flame. Actually, in the case of fluorine, for example, it will be found that for a given. fluorine content in the resultant frit, the fluorine contained in the raw batch fed to the electric smelter must be considerably less than in the raw batch smelted by means of a flame. It has been shown by actual analysis that only about /3 as much fluorine is lost when operating our electric smelter as occurs when smelting the same raw batch mixture by means of a flame.

Other modes of applying the principle of the out the heated gases eventing the possibility of any finely divided material from; entering 1 invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

We therefore particularly point out and distinctly claim as our invention:

1. A smelter for the continuous production of porcelain enamel comprising adjacent melting, smelting and fining chambers, the hearth of said melting chamber being of substantially lower elevation than the hearths of said smelting and fining chambers, a single large unrestricted passageway for molten material and hot gases connecting said melting and smelting chambers, separate passages respectively for hot gases and molten material connecting said smelting and fining chambers, a discharge passage for finished material in said fining chamber, a plurality of electrodes in each of said chambers, a separate power circuit to each group of said electrodes, each of said power circuits sufficient to supply an electric current through said groups of electrodes to effect a heating current flow through a mass of porcelain enamel forming materials and a flue opening in said smelting chamber.

2. A smelter for the continuous production of porcelain enamel comprising adjacent melting, smelting and fining chambers, the hearth of said melting chamber being of substantially lower elevation than the hearths of said smelting and fining chambers, a single large unrestricted passageway for molten material and hot gases connect- 8 ing said melting'and smelting chambers, separate passages respectively for hot gases and molten material connecting said smelting and fining chambers, a discharge passage for finished material in said fining chamber, a pair of horizontal electrodes disposed opposite each other in the side walls and below the normal bath level in said fining chamber, a separate power circuit to each group of said electrodes sufficient to supply an electric current through said groups of electrodes to effect a heating current flow through a mass of porcelain enamel forming materials and a flue opening in said smelting chamber.

ROBERT E. SKINNER. GLENN H. McINIYRE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,352,387 Saunders Sept. 7, 1920 1,552,555 Gravel Sept. 8, 1925 1,799,371 Hither Apr. 7, 1931 1,815,977 Hitner July 28, 1931 1,889,516 McIntosh Nov. 29, 1932 1,944,855 Wadman Jan. 23, 1934 2,040,215 Rava May 12, 1936 2,122,469 Hitner July 5, 1938 2,198,304 Cornelius Apr. 23, 1940 2,283,188 Cornelius May 19, 1942 2,559,683 Skinner et a1 July 10, 1951 2,610,217 Skinner et al Sept. 9, 1952 

